A reverse osmosis membrane and a preparation method and application thereof

Abstract

The application discloses a reverse osmosis membrane and a preparation method and application thereof, and the method comprises the following steps: wetting a hydrophobic membrane with an organic solvent, and then immersing the hydrophobic membrane in a modified monomer aqueous solution; wherein the modified monomer is one or more of m-phenylenediamine, aniline, o-phenylenediamine and p-phenylenediamine; an oxidizing agent is added into the modified monomer aqueous solution, and then stirring and standing are sequentially performed; the modified membrane is taken out and washed with water; and an active layer is prepared on the surface of the washed modified membrane through an interfacial polymerization reaction. The reverse osmosis membrane prepared by the application has excellent separation performance and long-term operation stability, can greatly reduce the cost of the reverse osmosis membrane, and has certain application potential in brackish water desalination and seawater desalination.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis membrane materials, and more particularly to a reverse osmosis membrane, its preparation method, and its application. Background Technology

[0002] Thin-layer composite (TFC) polyamide membranes, including reverse osmosis (RO), nanofiltration (NF), and forward osmosis (FO) membranes, are widely used in seawater and brackish water desalination, wastewater reuse, and resource extraction. TFC membranes mainly consist of two parts: a porous support layer, typically made of polysulfone or polyethersulfone, and an ultrathin, highly cross-linked polyamide active layer formed by interfacial polymerization of two aromatic monomers on the support layer. However, conventional polysulfone and polyethersulfone support layers are costly and not resistant to organic solvents; a large support layer thickness also results in a lower packing density of the TFC membrane in the membrane module, limiting production efficiency; furthermore, a high support layer thickness can lead to severe internal concentration polarization during forward osmosis, significantly inhibiting the forward osmosis water flux.

[0003] Polyethylene (PE) microporous membranes are commonly used as separators in lithium-ion batteries. Due to their excellent mechanical and chemical stability, high surface porosity, extremely low cost, and ultra-thin thickness, they have been considered a promising support layer for TFC membranes in recent years. However, the strong hydrophobicity of PE membranes prevents them from being wetted by an aqueous phase during interfacial polymerization, thus hindering the formation of an active layer on their surface. Although researchers have conducted extensive studies on the hydrophilic modification of PE membranes, including polymer and particulate hydrophilic coatings, surface grafting, and oxygen plasma treatment, these methods often suffer from problems such as cumbersome procedures, complex equipment, high costs, damage to polyethylene materials, toxic or harmful modifiers, and uneven or unstable modification. Exploring simple, economical, and reliable hydrophilic modification methods for PE membranes is of great significance for promoting the large-scale application of PE-supported TFC membranes. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a reverse osmosis membrane, its preparation method and application, aiming to significantly reduce the cost of existing commercial reverse osmosis membranes and promote the wider application of reverse osmosis membranes.

[0005] Poly(m-phenylene diamine) (PMPD) is a conjugated polymer that can be easily obtained through the chemical oxidative polymerization of m-phenylene diamine (MPD). Due to its strong chelating ability, redox capabilities, simple preparation, and low production cost, PMPD prepared by chemical oxidative polymerization has attracted considerable attention in adsorbent preparation. However, research on the application of PMPD in membrane separation is still very limited, and there are currently no studies on its use for hydrophilic modification of hydrophobic membranes. The abundant polar groups (such as amino and imino groups) in PMPD make it a potential candidate for hydrophilic modification of hydrophobic substrates in a simple and economical manner, but its feasibility needs to be proven. More importantly, interfacial polymerization requires the substrate to have suitable hydrophilicity and structural characteristics (pore size, porosity, surface roughness, etc.). Whether interfacial polymerization can be successfully carried out on the surface of PMPD-modified substrates to prepare high-performance TFC membranes is also unknown and worthy of further exploration.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a reverse osmosis membrane, comprising the steps of:

[0008] The hydrophobic membrane is wetted with an organic solvent and then immersed in an aqueous solution of a modified monomer; wherein the modified monomer is one or more of m-phenylenediamine, aniline, o-phenylenediamine and p-phenylenediamine;

[0009] An oxidant was added to the aqueous solution of the modified monomer, and then the mixture was stirred and allowed to stand. The modified membrane was then removed and rinsed with water.

[0010] An active layer was prepared on the surface of the modified membrane after rinsing via interfacial polymerization.

[0011] Optionally, the hydrophobic membrane is one of polyethylene microporous membrane, polypropylene membrane, polyvinylidene fluoride membrane, and polytetrafluoroethylene membrane;

[0012] The thickness of the hydrophobic film is 5-200 μm.

[0013] Optionally, the organic solvent is one or more of ethanol, methanol, isopropanol, and acetone.

[0014] Optionally, the oxidant is persulfate, hydrogen peroxide, silver nitrate, or Fe. 3+ Cu 2+ Ni 2+ One or more of them;

[0015] The persulfate is one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0016] Optionally, the concentration of the modified monomer aqueous solution is 0.001-50 wt%.

[0017] Based on a system consisting of a modified monomer aqueous solution and an oxidant, the concentration of the oxidant is 0.001-50 wt%.

[0018] Optionally, the stirring time is 0.1-600 minutes, and the settling time is 1 minute-120 hours.

[0019] Optionally, the method for preparing the reverse osmosis membrane specifically includes the following steps:

[0020] The polyethylene microporous membrane was wetted with ethanol and then immersed in an aqueous solution of m-phenylenediamine.

[0021] Persulfate was added to the aqueous solution of m-phenylenediamine, and then the mixture was stirred and allowed to stand. The modified membrane was then removed and rinsed with water.

[0022] An active layer was prepared on the surface of the modified membrane after rinsing via interfacial polymerization.

[0023] Optionally, the active layer is a polyamide active layer, and the method for preparing the polyamide active layer on the surface of the modified membrane after rinsing via interfacial polymerization specifically includes the following steps:

[0024] First, add an aqueous solution containing m-phenylenediamine to the surface of the modified membrane after rinsing. After a few minutes, remove the aqueous solution and blow dry the residual aqueous solution on the surface of the modified membrane.

[0025] Then, an organic solution containing pyromellitic methyl chloride was added to the surface of the dried modified film. After a few minutes, the organic solution was removed and the film was left to stand in the air.

[0026] Finally, the polyamide active layer is obtained on the surface of the modified film through heat treatment.

[0027] A reverse osmosis membrane, wherein the membrane is prepared by the preparation method described in this invention.

[0028] An application of a reverse osmosis membrane as described in this invention in brackish water desalination and seawater desalination.

[0029] Beneficial Effects: This invention provides a reverse osmosis membrane, its preparation method, and its applications. The method includes the following steps: wetting a hydrophobic membrane with an organic solvent, then immersing it in an aqueous solution of a modified monomer, ensuring direct contact between both sides of the membrane and the solution. An oxidizing agent, such as persulfate, is added to the modified monomer aqueous solution, the solution is gently stirred for a few minutes, and then allowed to stand at room temperature for a period of time to obtain the modified membrane. The modified membrane is thoroughly rinsed with deionized water. Finally, an interfacial polymerization reaction is performed on the surface of the modified membrane to form an ultrathin and dense active layer. The reverse osmosis membrane prepared by this invention exhibits excellent separation performance and long-term operational stability, significantly reducing the cost of reverse osmosis membranes and demonstrating potential applications in brackish water desalination and seawater desalination. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating a preferred embodiment of the preparation of a reverse osmosis membrane according to the present invention.

[0031] Figure 2 The images show the original and PMPD-modified PE films in Example 1.

[0032] Figure 3 The images shown are SEM images of the original and PMPD-modified PE films in Example 1.

[0033] Figure 4 The diagram shows the NaCl rejection rate and pure water permeability coefficient of the RO membrane prepared in Example 1.

[0034] Figure 5 The graph shows the changes in NaCl rejection rate and water flux of the RO membrane prepared in Example 1 as a function of filtration time. Detailed Implementation

[0035] This invention provides a reverse osmosis membrane, its preparation method, and its applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0036] Please see Figure 1 The present invention provides a preferred embodiment of a method for preparing a reverse osmosis membrane, as shown in the figure, including the following steps:

[0037] S1. Wet the hydrophobic membrane with an organic solvent and then immerse it in an aqueous solution of the modified monomer; wherein the modified monomer is one or more of m-phenylenediamine, aniline, o-phenylenediamine and p-phenylenediamine;

[0038] S2. Add an oxidant to the modified monomer aqueous solution, then stir and let stand in sequence, and take out the modified membrane and rinse it with water.

[0039] S3. An active layer is prepared on the surface of the modified membrane after rinsing via interfacial polymerization.

[0040] The method of this embodiment includes the following steps: wetting a hydrophobic membrane with an organic solvent, then immersing it in an aqueous solution of a modified monomer, so that both sides of the membrane are in direct contact with the solution. An oxidant such as persulfate is added to the aqueous solution of the modified monomer, the solution is gently stirred for a few minutes, and then allowed to stand at room temperature for a period of time to obtain a modified membrane. The modified membrane is thoroughly rinsed with deionized water. Finally, an interfacial polymerization reaction is carried out on the surface of the modified membrane to form an ultrathin and dense active layer. The reverse osmosis membrane prepared in this embodiment has excellent separation performance and long-term operational stability, which can significantly reduce the cost of reverse osmosis membranes and shows certain application potential in brackish water desalination and seawater desalination.

[0041] In one embodiment, the hydrophobic membrane (as a substrate) can be, but is not limited to, a polyethylene microporous membrane, and can also be selected from other hydrophobic membranes, such as polypropylene membranes, polyvinylidene fluoride membranes, or polytetrafluoroethylene membranes. Preferably, the hydrophobic membrane is a polyethylene microporous membrane.

[0042] In one embodiment, the thickness of the hydrophobic film is 5-200 μm, preferably 5-100 μm, more preferably 5-50 μm, for example 5 μm, 10 μm, 20 μm, 40 μm, 50 μm.

[0043] In one embodiment, the hydrophobic membrane is a polyethylene microporous membrane with a thickness of 5-20 μm, such as 5 μm, 10 μm, 15 μm, or 20 μm.

[0044] In one embodiment, the organic solvent used to wet the hydrophobic membrane can be one or more of ethanol, methanol, isopropanol, and acetone. Preferably, the organic solvent used to wet the hydrophobic membrane is ethanol.

[0045] In one embodiment, the oxidant can be, but is not limited to, persulfate, and can also be hydrogen peroxide, silver nitrate, or Fe. 3+ Cu 2+ Ni 2+ Or any combination thereof. Preferably, the oxidant is a persulfate. The persulfate may be, but is not limited to, one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0046] In one embodiment, the concentration of the modified monomer aqueous solution is 0.001-50 wt%, preferably 0.001-10 wt%, more preferably 0.001-0.1 wt%, such as 0.05 wt%.

[0047] In one embodiment, based on a system consisting of a modified monomer aqueous solution and an oxidant, the concentration of the oxidant is 0.001-50 wt%, preferably 0.001-20 wt%, more preferably 0.001-1 wt%, such as 0.001 wt%, 0.038 wt%, 0.1 wt%, 0.5 wt%, or 1 wt%.

[0048] In one embodiment, the stirring time is 0.1-600 minutes, preferably 0.1-100 minutes, more preferably 0.1-50 minutes, such as 0.1 minutes, 1 minute, 5 minutes, 10 minutes, 30 minutes, and 50 minutes.

[0049] In one embodiment, the settling time is 1 min to 120 h, preferably 1 min to 60 h, more preferably 1 h to 30 h, such as 1 h, 5 h, 10 h, 15 h, 20 h, or 30 h.

[0050] In one embodiment, the method for preparing the reverse osmosis membrane includes the following steps:

[0051] The polyethylene microporous membrane was wetted with ethanol and then immersed in an aqueous solution of m-phenylenediamine.

[0052] Persulfate was added to the aqueous solution of m-phenylenediamine, and then the mixture was stirred and allowed to stand. The modified membrane was then removed and rinsed with water.

[0053] An active layer was prepared on the surface of the modified membrane after rinsing via interfacial polymerization.

[0054] The method of this embodiment includes the following steps: A polyethylene (PE) microporous membrane is wetted with ethanol and then immersed in an aqueous solution of m-phenylenediamine, ensuring direct contact between both sides of the membrane and the solution. An oxidizing agent, persulfate, is added to the m-phenylenediamine aqueous solution, and the solution is gently stirred for a few minutes, then allowed to stand at room temperature for a period of time. The modified membrane is then thoroughly rinsed with deionized water. Finally, an interfacial polymerization reaction is performed on the surface of the modified membrane to form an ultrathin, dense active layer. The reverse osmosis membrane prepared in this embodiment exhibits excellent separation performance and long-term operational stability, significantly reducing the cost of reverse osmosis membranes and demonstrating potential applications in brackish water desalination and seawater desalination.

[0055] Specifically, see Figure 2 In this embodiment, the polyethylene microporous membrane is first wetted with ethanol to allow the m-phenylenediamine aqueous solution to fully penetrate the membrane pores. Then, the PE membrane is immersed in the m-phenylenediamine aqueous solution, ensuring direct contact between both sides of the membrane and the solution. This results in similar modification effects on both sides and better modification of the membrane's interior. Persulfate, an oxidizing agent, is added to the m-phenylenediamine aqueous solution to accelerate the MPD oxidative polymerization process. The solution is gently stirred for several minutes to ensure homogenization, and then allowed to stand at room temperature for approximately 10 hours to allow MPD to undergo in-situ chemical oxidative polymerization on the PE fiber surface, forming a PMPD coating and achieving hydrophilic modification of the PE membrane. The modified membrane is then removed and thoroughly rinsed with deionized water. An active layer is prepared on the modified membrane surface via interfacial polymerization.

[0056] In one embodiment, the active layer is a polyamide active layer, and the method for preparing the polyamide active layer on the surface of the modified membrane after rinsing via interfacial polymerization specifically includes the following steps:

[0057] First, add an aqueous solution (aqueous phase) containing m-phenylenediamine to the surface of the modified membrane after rinsing. After a few minutes, remove the aqueous phase and blow dry the residual aqueous phase on the surface of the modified membrane.

[0058] Then, an organic solution (oil phase) containing pyromellitic methyl chloride was added to the surface of the dried modified film. After a few minutes, the oil phase was removed and the film was left to stand in the air.

[0059] Finally, the polyamide active layer is obtained on the surface of the modified film by heat treatment (the purpose of which is to further improve the crosslinking degree of the polyamide active layer).

[0060] In one embodiment, the aqueous solution containing m-phenylenediamine may also contain an additive, which may be one or more of, but not limited to, sodium dodecyl sulfate, camphor sulfonic acid, triethylamine, and dimethyl sulfoxide.

[0061] In one embodiment, the aqueous monomer for interfacial polymerization can be, but is not limited to, m-phenylenediamine, or piperazine.

[0062] In one embodiment, the oil phase is prepared by dissolving trimesoyl chloride in an organic solvent. In one embodiment, the organic solvent may be, but is not limited to, n-hexane, or may be an Isopar series solvent, toluene, xylene, ethyl acetate, or a mixture thereof.

[0063] This invention also provides a reverse osmosis membrane, which is prepared using the preparation method described in this invention.

[0064] Preferably, the reverse osmosis membrane is a polyamide reverse osmosis membrane supported by a poly(m-phenylene diamine) modified polyethylene membrane.

[0065] This invention also provides an application of a reverse osmosis membrane, wherein the reverse osmosis membrane prepared by the above method is applied to brackish water desalination or seawater desalination.

[0066] The present invention will be further explained and illustrated below through specific embodiments.

[0067] Example 1

[0068] The preparation method of the polyamide reverse osmosis membrane supported by poly(m-phenylene diamine) modified polyethylene membrane in this embodiment includes the following steps:

[0069] The polyethylene microporous membrane was wetted with ethanol and then immersed in a 0.05 wt% aqueous solution of m-phenylenediamine (MPD), ensuring direct contact between both sides of the membrane and the solution. Sodium persulfate, an oxidizing agent, was added to the MPD aqueous solution to achieve a concentration of 0.038 wt%. The solution was gently stirred for a few minutes and then allowed to stand at room temperature for 10 hours. The modified membrane (i.e., the poly(m-phenylenediamine) modified polyethylene membrane) was then removed and thoroughly rinsed with deionized water.

[0070] An active layer was prepared on the surface of a modified membrane via interfacial polymerization. First, an aqueous solution (aqueous phase) containing 2.0 wt% m-phenylenediamine, 0.05 wt% sodium dodecyl sulfate, 0.8 wt% camphor sulfonic acid, 1.1 wt% triethylamine, and 2.0 wt% dimethyl sulfoxide was poured onto the surface of the modified membrane. After 5 minutes, the aqueous phase was discarded, and the remaining aqueous phase on the membrane surface was dried with nitrogen. Then, an oil phase solution (n-hexane) containing trimesoyl chloride (TMC) was poured onto the membrane surface. After 3 minutes, the oil phase was discarded, and the membrane was allowed to stand in air for 2 minutes. Finally, the membrane was heat-treated in a 60°C oven for 10 minutes, then removed and stored in deionized water.

[0071] Tests were conducted on the pure water flux, pure water permeability coefficient, and salt rejection rate of the reverse osmosis membrane prepared in Example 1.

[0072] The pure water flux (J) is calculated using the following formula. w ):

[0073]

[0074] Δm is the mass of the permeate during time interval Δt, ρ w S is the density of water. m The effective membrane area. The pure water permeability coefficient (A) is the pure water flux divided by the pressure (P):

[0075]

[0076] Salt rejection rate (R value) is calculated based on the salt concentration of the bulk feed solution (c). f ) and permeate salt concentration (c p ):

[0077]

[0078] Figure 2 The images show the original PE film (left) and the PMPD-modified PE film (right) in Example 1.

[0079] Figure 3 These are SEM images of the original PE film (left) and the PMPD-modified PE film (right) in Example 1. From... Figure 3 It can be seen that the original PE membrane exhibits a microporous structure composed of interconnected nanoscale wide PE fibers. After modification, the PE fibers are wrapped by PMPD, the pores on the surface of the PE membrane are slightly reduced, and the modification maintains the microporous structure of the membrane.

[0080] Figure 4 This is a graph showing the NaCl rejection rate and pure water permeability coefficient of the RO membrane prepared in Example 1. From... Figure 4 It can be seen that the prepared RO membrane has an excellent NaCl rejection rate of 99.3±0.1% and a pure water permeability coefficient of 1.3±0.2 L / m.-2 h -1 bar -1 (LMH / bar).

[0081] Figure 5 This is a graph showing the changes in NaCl rejection rate and water flux of the prepared RO membrane with filtration time in Example 1. From... Figure 5 It can be seen that the prepared RO membrane maintained its water flux and high NaCl rejection rate well during the long-term operation of 240h, proving that the prepared RO membrane has excellent long-term operational stability.

[0082] In summary, this invention utilizes in-situ chemical oxidative polymerization of m-phenylenediamine on the surface of PE fibers to form a poly-m-phenylenediamine coating rich in polar groups. This achieves simple and effective hydrophilic modification of the PE membrane at low cost, significantly reducing the water transport resistance of the PE membrane. Furthermore, it allows the interfacial polymerized aqueous monomers to wet the PE membrane and distribute uniformly, resulting in a complete and defect-free polyamide active layer. The reverse osmosis membrane prepared by this invention exhibits excellent separation performance and long-term operational stability, significantly reducing the cost of reverse osmosis membranes and demonstrating potential applications in brackish water desalination and seawater desalination.

[0083] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that, Including the following steps: A polyethylene microporous membrane was wetted with an organic solvent and then immersed in an aqueous solution of a modified monomer; the modified monomer was m-phenylenediamine. An oxidant is added to the aqueous solution of the modified monomer, and then the mixture is stirred and allowed to stand in situ to allow the modified monomer to undergo oxidative polymerization on the surface of the polyethylene microporous membrane to form a poly(m-phenylene diamine) coating, thereby obtaining a modified membrane. The modified membrane is then removed and rinsed with water. An active layer is prepared on the surface of the modified membrane after rinsing via interfacial polymerization to obtain the reverse osmosis membrane; The thickness of the polyethylene microporous membrane is 5-200 μm; The organic solvent is one or more of ethanol, methanol, isopropanol, and acetone; The oxidant is persulfate, hydrogen peroxide, silver nitrate, or Fe. 3+ Cu 2+ Ni 2+ One or more of them; The persulfate is one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; The concentration of the modified monomer aqueous solution is 0.001-50 wt%; Based on a system consisting of a modified monomer aqueous solution and an oxidant, the concentration of the oxidant is 0.001-50 wt%; The stirring time is 0.1-600 minutes, and the settling time is 1 min-120 h; The active layer is a polyamide active layer. The method for preparing the polyamide active layer on the surface of the modified membrane after rinsing via interfacial polymerization reaction specifically includes the following steps: First, add an aqueous solution containing m-phenylenediamine to the surface of the modified membrane after rinsing. After a few minutes, remove the aqueous solution and blow dry the residual aqueous solution on the surface of the modified membrane. Then, an organic solution containing pyromellitic methyl chloride was added to the surface of the dried modified film. After a few minutes, the organic solution was removed and the film was left to stand in the air. Finally, the polyamide active layer is obtained on the surface of the modified film through heat treatment.

2. A reverse osmosis membrane, characterized in that, It was prepared using the preparation method described in claim 1.

3. The application of the reverse osmosis membrane as described in claim 2 in brackish water desalination and seawater desalination.

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